In order to check and measure the damage to crashed cars before, during and after repair, telescopically extendable measuring devices or rulers provided with perpendicularly upwards extending mandrels in both ends are used. A ruler that is provided with a magnetic fastening bracket in one end (SE 9704438-2) is also used in this type of application. These devices are simple, easy to handle and result in surprisingly highly precise work. In reality, however, these devices require writing down or remembering measurements between device measures. Furthermore, the precision of these devices is dependent on the skill or measuring technique of the device operator, since inclining the ruler may change the result. Likewise, operator skill and environmental conditions when reading scales are of essential influence.
An additional error source in prior art measuring rulers is that the magnet fastener, which allows fast and simple handling of the device by one person even for long measurements, is prone to mounting that introduces a slight error. Mounting the prior art device in different ways on the left and right side can give different measures even if the measure should be the same. In addition, a little dirt under the magnet gives an inclination the fastener that may cause the device to mis-measure.
Thus, the object of this invention is to create a measuring device that overcomes the above problems with the prior art devices without impairing the simplicity and ease of use of the device.
In accordance with the invention, a telescopically extendable ruler is provided with measurement mandrels or suitable measurement bodies in the ends, the ruler being provided with a digital measuring means. The previous scale is thus replaced with an electronic measuring apparatus and indication of the measure. In this way, it is no longer necessary that the user is in the precisely correct place on the side of the measuring device in order to see the scale. Further, the risk that a user might shadow the scale thereby being unable to read the device is also reduced and, since the device stores measured values, values are ready for comparison, even if several minutes lapse between measurements. If so desired, one can measure absolute values or measure differences between measures taken on an undamaged area of the car, and a measure taken on a damaged area. The later type of technique facilitates, in particular, measurements taken during straightening operations. It is also easier to remember small figures than larger ones.
The present invention also joins the ruler to a centering mandrel or cone, while a magnet placed over the cone is moveable. By additionally making the ruler moveable about a universal joint, the ruler can be centered within a hole, from where measurements are to be taken. Thus, the measurements of the current device will not be influenced by the inclination of the magnet, caused by a locally dented surrounding, dirt, underbody coating, etc.
Since the force that the centering mandrel or cone is subjected to is exclusively directed towards, a vehicle, the centering tip or cone, which is journaled on a ball, can be provided with some type of snap lock so than one simply snaps the conical tip on the universal joint. In this way one can use different cones of varying length depending on the size of the hole. Thus, it is actually possible to place the universal joint precisely in the center of the hole. One can also contemplate the use of other types of points or tips.
In order further to simplify the current device, the device is provided with an adjustable spirit level on the side or on top of the ruler, extending along the length of the ruler. In this way it becomes possible to take a measurement between two known and undamaged points in the longitudinal direction of the car. The measuring mandrel located at the outer end of the ruler is adjusted to the height required to give an orientation to the ruler parallel to the datum plane of the car. The spirit level is now adjusted to an entirely level position. The spirit level together with its fastening bracket is then turned 180xc2x0 and then the entire ruler is turned or moved so that its ends change position in relation to the vehicle that is to be measured. The spirit level will now, with the ruler placed lengthwise along the car, represent a definition of the datum plane of the vehicle, allowing quick and normalized measuring. A supposition for this is that the vehicle stands comparatively even laterally, but since this normally is the case, it is not a problem. However, it is more common that the vehicle is inclined in its length direction.
The electronic digital measuring of the extension of the ruler is preferably done by means of a device located in one of the telescoping tubes. The device comprises a thin metal tape that is fastened in the other end of the ruler. The tape runs over a rotatable drum. A spring device is arranged to pretension the drum so that the tape always is kept stretched. The extended length is then detected by the drum or roller for the tape having a toothed or screen pattern provided wheel that passes between a light source and a photo detector generating pulses as the drum or wheel rotates and the pulses can then simply be counted and transformed to measures shown on a display in the end of the ruler, either in millimeters or in inches.